Effects of lesioning of the substantia innominata on autoregulation of local cerebral blood flow in rats.

Recently, accumulated data have suggested that the nucleus basalis magnocellularis, i.e., the substantia innominata (SI), may represent the primary source of central cholinergic innervation in the rat cortical vasculature. We therefore examined the effects of unilateral lesion of the SI on the autoregulation of local CBF (lCBF) during induced hypotension in rats. Male Wistar rats were divided into three groups. The animals of groups 1 and 2 received an injection of 5 micrograms of ibotenate into the right SI stereotaxically. At 7 days after the injection, the lCBF was measured by the [14C]iodoantipyrine technique in the awake state. Group 1 was used as the normotensive group (MABP = 113.1 +/- 12.2 mm Hg). Group 2 formed the hypotensive group, and the lCBF was measured during hypotension (MABP = 80.0 +/- 5.5 mm Hg) induced by hemorrhage. Group 3, the sham-operated normotensive group, received vehicle injection into the right SI at 7 days prior to the lCBF measurement. In group 1, lCBF was significantly lower in the frontal, parietal, temporal, and striate cortices on the lesioned side compared to that on the contralateral side. In group 2, lCBF was significantly decreased in the cortices on the lesioned side, but there was no significant difference in magnitude of the lCBF reduction between groups 1 and 2. Group 3 exhibited no hemispheric asymmetries in lCBF. These findings suggest that the SI exerts an influence on cortical lCBF, but does not play a role in the autoregulation of lCBF during hypotension.